There is only one 25 pfennig coin in the history of coins after 1871. I bouhgt a good example from the most common date for 11, it is rather nice. So, if you have a coin not in too good a condition then it will probably be worth nothing more than 6 which is like $8 US I think. Though if you are not in the german market it might not be so easy to sell for that price.
If you have a rarer date, then you could be in for a little more, I think 90 was the most expensive in great condition.
1, 5 and 10 coins are available for cheap prices, around 1 to 2 for almost all examples, again, dates and mintmarks will change the price. There are some post war coins made of zinc, that took the nazi design but did away with the swastika (hakenkreuz) and these can be a little more, 5p and 10p are around 6-10 for an ok example, 1p is a little more expensive.
However for the 50 cent, these coins are more expensive.
If you have the k๖nigreich coins then 50 cent is likely to be minimum 25, if you have weimar there are some expensive examples, you will not have the 1925-26 50 cent which says reichspfennig, if you do, it would be worth 1000 or more.
The renntenpfennig version can be got for 12 in worst condition most numerous mint and date mark but can go quite high.
However more probably you have some of the not so expensive later versions, there are quite a few designs.